1. Field of the Invention
This invention relates to a power-steering system for a vehicle.
2. Description of the Prior Art
There has been known a power-steering system for a vehicle in which the assisting force is reduced with increase in the vehicle speed so that when the vehicle speed is low or zero, the steering wheel can be easily turned, and when the vehicle speed is high, immoderate turn of the steering wheel is prevented.
Generally, the normal vehicle in which the front wheels are dirigible is apt to yaw and loose running stability when it runs rearward unlike when it runs forward. In this conjunction, the conventional power-steering system in which the rate of reducing the assisting force with increase in the vehicle speed is the same irrespective of whether the vehicle is driven in reverse or forward is disadvantageous in that it does not contribute to suppressing occurrence of yaw of the vehicle body when the vehicle runs rearward.